Method for preparing alternating copolymers using a friedel-crafts catalyst and a free radical initiator in an aqueous medium

ABSTRACT

An improved method for preparing 1:1 alternating copolymers by reacting an electron donor monomer and an electron acceptor monomer in an aqueous medium in the presence of a Friedel-Crafts halide and a water-soluble free radical initiator.

United States Patent 1 1 u 1 3,864,319

Gaylord Feb. 4, 1975 METHOD FOR PREPARING ALTERNATING [58] Field ofSearch 260/835, 82.5, 82.3

COPOLYMERS USING A FRIEDEL-CRAFTS CATALYST AND A FREE RADICAL 1 1References Cited INITIATOR IN AN AQUEOUS MEDIUM UNITED STATES PATENTS 75Inventor; Norman Gayhrd, New 3,637,611 1/1972 Takeya et al. 260/785 N3,647,753 3/1972 Nakaguchi et alv 260/63 R Pmvdence 3,700,637 10 1972Finch 260/833 [73} Assignee: Gaylord Research Institute, Inc.,

Newark, NJ. Primary ExaminerWilliam F. Hamrock [22] Filed Nov 1 1972Attorney, Agent, or FirmLawrence Rosen; E. Janet Berry [21] Appl. No.:302,964

Related US. Application Data d th d f T 1 1 h t n improve me 0 orpreparing a erna mg c0- [63] fg g sg xg of polymers by reacting anelectron donor monomer and an electron acceptor monomer in an aqueousmedium U S 3 5 5 III the presence Of a FIIedel-Crafts and a water-IMO/85:5 1260/2367 soluble free radical initiator. [51] Int. Cl. C08d1/09, C08d 1/18, C08d l/22 9 Claims, No Drawings METHOD FOR PREPARINGALTERNATING COPOLYMERS USING A FRlEDEL-CRAFTS CATALYST AND A FREERADICAL INITIATOR IN AN AQUEOUS MEDIUM This application is acontinuation-in-part of Ser. No. 66,887, filed Aug. 25, I970, nowabandoned.

The present invention relates to a novel method for the preparation ofalternating copolymers by the copolymerization of electron donormonomers with electron acceptor monomers. More specifically, theinvention pertains to the preparation of high molecular weight equimolaralternating copolymers from non-polar monoolefins or multiolefins andpolar electron acceptor monomers in an aqueous medium.

The copolymerization of a monomer containing strongly electron donatingsubstituents with a monomer containing strongly electron withdrawingsubstituents yields an essentially alternating copolymer, that is, acopolymer in which the comonomer units are present in essentiallyequimolar quantities and are situated alternately along the copolymerchain. Alternating copolymers are also produced by the copolymerizationof an electron donating monomer with an electron acceptor which does notreadily undergo homopolymerization. Thus, alternating copolymers areproduced, for example, from the copolymerization of the electron donormonomers, styrene and butadiene with the electron acceptors, vinylidenecyanide, maleic anhydride and sulfur dioxide.

The complexation of a moderately or weakly electron accepting monomercontaining pendant carbonyl, carboxylate, carboxamide or nitrile groupswith a Friedel-Crafts catalyst, Lewis acid or organo-aluminum halideincreases the electron accepting characteristics of the monomer, and oncopolymerization with an electron donor monomer, yields alternatingcopolymers. Thus, complexation of methyl acrylate, methyl methacrylateor acrylonitrile with zinc chloride, aluminum chloride, borontrifluoride, ethyl aluminum dichloride or ethyl aluminum sesquichloridepermits the formation of alternating copolymers with butadiene,isoprene, styrene, ethylene, propylene and higher alphaolefins.

The preparation of alternating copolymers from electron donor monomersand electron acceptor monomers as a result of complexation of theelectron acceptor monomers may be carried out in the absence as well asin the presence of an organic free radical initiator in bulk, or in aninert hydrocarbon or halogenated hydrocarbon solvent such as benzene,toluene, hexane, carbon tetrachloride, chloroform, etc. (N. G. Gaylordand H. Antropiusova, Journal of Polymer Science, Part B, 7, I45 (1969)and Macromolecules, 2, 442 (1969); A. Takahashi and N. G. Gaylord,Journal of Macromolecular Science (Chemistry), A4, 127 (1970),

A process for the free radical initiated copolymerization of non-polarallylic and olefinic compounds with polar monomers, such asacrylonitrile and methyl methacrylate, in the presence ofaFriedel-Crafts halide such as zinc chloride, under anhydrous conditions,is described in US. Pat. No. 3,183,217. The copolymerization is carriedout in bulk or in an inert organic solvent.

An improved process by the same inventors, described in US. Pat. No.3,278,503, extends the process to the copolymerization of Cs-C diolefinsunder anhydrous conditions and discloses that excess polar monomer isthe preferred diluent for both monoolefin and diolefin free radicalinitiated copolymerization with polar monomers which are complexed witha Friedel- Crafts halide.

The formation of alternating copolymers from the copolymerization of anolefin, halogenated olefin or multiolefin with an acrylic monomer in thepresence of an organoaluminumm or organoboron halide and, if necessary,in the presence of oxygen or an organic peroxide, is disclosed inBritish Pat. No. l,l23,724 and earlier British Patents by the sameinventors referred to therein. The copolymerization is carried out inliquid monomer or in inert solvents such as hydrocarbons orhalogen-containing hydrocarbons.

The prior art clearly teaches that the copolymerization of non-polarmonomers with polar monomers in the presence of a Friedel-Craftscatalyst and, where necessary, oxygen or an organic peroxide, requiresanhydrous, preferably non-polar, media.

It has now been discovered that alternating copolymers can be preparedfrom electron donor monomers and electron acceptor monomers in thepresence of a suitable Friedel-Crafts catalyst and a water-soluble freeradical initiator in an aqueous medium.

The electron donor monomers are typically acyclic and cyclic monoolefinsand conjugated dienes. The monoolefins may be alpha-olefins or internalolefins including cycloolefins and may be unsubstituted or may containalkyl, aryl or aralkyl substituents. The effective alpha-olefins includel-alkenes such as ethylene, propylene, l-butene, l-pentene, l-hexene,l-heptene, loctene, l-nonene, l-decene, l-undecene, l-dodecene,l-tridecene, l-tetradecene, l-pentadecene, lhexadecene, l -heptadecene,l-octadecene, lnonadecene, l-eicosene, l-heneicosene, l-docosene,ltricosene, l-tetracosene and other l-alkenes containing up to 40 carbonatoms. Other alpha-olefins which are useful in the process of thisinvention are substituted l-alkenes having the following structuralformula CH =C (CH I-I where R is an alkyl moiety containing 1 to 8carbon atoms and n is an integer from 1-40 and include isobutylene,2-methyl-l-butene, 2-methyl-l-pentene, Z-methyl-l-hexene,Z-methyI-l-heptene, Z-methyl-loctene, 2-methyl-l-nonene,Z-ethyl-I-pentene, 2-ethyll-hexene, 2-ethyl-l-heptene,2-propyl-l-hexene, 2' butyl-l-nonene, 2-isopropyl-l-octene and the like.1- Alkenes having substituents further removed from the double bond areeffective and include 3-methyl-lpentene, 4-methyl-l-pentene,3-methyl-l-hexene, S-methyl-l-hexene and the like. Aromatic substitutedalpha-olefins are particularly effective electron donor monomers andinclude styrene, alpha-methylstyrene, p-methylstyrene, o-methylstyrene,m-methylstyrene, p-ethylstyrene, p-propylstyrene, p-isopropylstyrene,pbutylstyrene, p-nonylstyrene, p-chlorostyrene, and other l-alkenescontaining alkyl substituted aromatic moieties. Similarly, alpha-olefinscontaining aromatic substituents further removed from the double bondsuch as 3-phenyl-l-butene, 4-p-methylphenyl-l' pentene and the like areeffective electron donor monomers.

Internal olefins which are useful electron donor monomers in the presentinvention may be unsubstituted alkyl or aryl substituted acyclic orcyclic monoolefins including 2-butene, Z-pentene. Z-hexene, 3- hexene,Z-heptene, 3-heptene, 2-octene, 3-octene, 4- octene. 2-nonene, 3-nonene,4-nonene, Z-methyl-Z- butene, 2-methyl-2-pentene, 4-methyl-2-pentene,2-methyl-2-hexene, 4-methyl'2-hexene, S-methyl-Z- hexene,2,5-dimethyl-3-hexene, l-phenyl-3-pentene, cyclopentene, cycloheptene,cyclooctene, cyclononene, cyclodecene, cycloundecene. cyclododecene,lmethylcycloheptene, S-methylcycloheptene and the like.

The conjugated dienes which are useful as electron donor monomers in theprocess of this invention comprise compounds having the followingstructural formula:

where R, R R and R which may be the same or different, represent amember of the group consisting of hydrogen, aryl, cycloalkyl or alkylradicals having from 1 to 40 carbon atoms, and preferably from about 1to 8 carbon atoms. Illustrative conjugated dienes include butadiene,isoprene, 2-chloro-l,3-butadiene, 2,3- dichloro-l ,B-butadiene,2,3-dimethylbutadiene, propylene, 2,4-hexadiene, 2-methyl-l,3-pentadiene, 2-ethyll,3-butadiene, 2-propyl-,l ,3-butadiene,Z-phenyl-l ,3- butadiene, 3-methyll ,3-pentadiene, 2-ethyl-l ,3-pentadiene, 2-methyl-l,3-hexadiene and the like. Cyclic conjugateddienes such as 1,3-cyclohexadiene, [,3- cycloheptadiene, l,3-cyclooctadiene, l ,3- cyclononadiene, l,3-cyclodecadiene,l,3cycloundecadiene, l,3-cyclododecadiene and the like are alsoeffective electron donor monomers.

The electron acceptor monomers typically contain carbonyl, carboxyl,carboxylate, carboxamide and nitrile groups. Thio analogues of theoxygen-containing functional groups are also effective electron acceptormonomers. Illustrative electron acceptor monomers include acrylic acid,acrylamide, acrylonitrile, alkyl acrylates in which the alkyl moietycontains 1 to 40 carbon atoms, preferably 1 to 22 carbon atoms,including methyl acrylate, ethyl acrylate, propyl acrylate, isopropylacrylate, butyl acrylate, isobutyl acrylate, sec-butyl acrylate, hexylacrylate, 2-ethylhexyl acrylate, heptyl acrylate, octyl acrylate,isooctyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate,dodecyl acrylate, tridecyl acrylate, pentadecyl acrylate, hexadecylacrylate, octadecyl acrylate and the like, aryl acrylates such as penylacrylate and ptolyl acrylate, cycloalkyl acrylates such as cyclohexylacrylate, methacrylic acid, methacrylamide, methacrylonitrile, alkylmethacrylates in which the alkyl moiety contains 1-40 carbon atoms,preferably 1 to 22 carbon atoms, including methyl methacrylate, ethylmethacrylate, propyl methacrylate, isopropyl methacrylate, butylmethacrylate, isobutyl methacrylate, sec-butyl methacrylate, amylmethacrylate, hexyl methacrylate, heptyl methacrylate, octylmethacrylate, Z-ethylhexyl methacrylate, nonyl methacrylate, decylmethacrylate, undecyl methacrylate, dodecyl methacrylate, tridecylmethacrylate, pentadecyl methacrylate, hexadecyl methacrylate, octadecylmethacrylate, and the like, aralkyl methacrylates such as benzylmethacrylate, aryl methacrylates such as phenyl methacrylate and p-tolylmethacrylate and cycloalkyl methacrylates such as cyclohexylmethacrylate as well as methyl vinyl ketone, ethyl vinyl ketone, methylisopropenyl ketone, acrolein, methacrolein and the like. The sulfurcontaining compounds which are effective electron acceptor monomersinclude thiocarboxylic acids such as thioacrylic acid andthiomethacrylic acid, thiocarboxamides such as thioacrylamide andthiomethacrylamide as well as alkyl, aryl, aralkyl and cycloalkylthiocarboxylates such as methyl thioacrylate, methyl thiomethacrylate,phenyl thioacrylate, benzyl thiomethacrylate, cyclohexylthiomethacrylate and the like. Dithioacrylic acid, dithiomethacrylicacid and the esters of these dithiocarboxylic acids are also usefulelectron acceptor monomers.

The Friedel-Crafts catalysts useful in carrying out the copolymerizationprocess of this invention are inert to water under the conditions ofpolymerization. Oxidizing salts or halides of metals which are at leastdivalent are preferred. Such catalysts include halides of zinc, nickel,magnesium, cerium, tin, zirconium, chromium, vanadium, titanium andmolybdenum. Oxyhalides or hydrates of such Friedel-Crafts catalysts areeffective catalysts. Typical metal compounds thus include zinc chloride,magnesium chloride, nickel chloride, ceric ammonium nitrate and thelike. Although amounts of the Friedel-Crafts catalysts may vary over awide range, the concentration is generally between 0.0l-5 moles per moleof electron acceptor monomer, preferably 005-] moles per mole.

The molar ratio of the electron donor monomer to the electron acceptormonomer will generally range from 5:95 to :5. The equimolar alternatingcopolymers are produced independent of comonomer ratio. For ease ofhandling the reaction mixture and to increase the reaction rate anexcess of one of the monomers is sometimes preferred.

The solubility or emulsifiability of one or more of the monomers inwater appears to play little or no role in the copolymerization reactionof the present invention. The copolymerization proceeds both in theabsence and in the presence of an emulsifier. The polymerizing specieswhich is believed to be a complex containing both monomers and thecomplexing agent is generally insoluble in the aqueous medium. Thealternating copolymer is also insoluble and therefore the reactionoccurs predominantly in a heterogeneous environment.

Although water is an inert ingredient in the present invention, thereaction is generally carried out with as little water as is practicalfor ease of handling. ln general, the amount of water will range fromten times to one tenth the volume of the monomers. The preferred amountof water is from three times to one third the volume of monomers.

The prior art teaches that the copolymerization of donor and acceptormonomers in the presence of a Friedel-Crafts catalyst or organoaluminumhalide is catalyzed by an organic peroxide or other organic free radicalprecursor. The use of an aqueous medium in the process disclosed hereindoes not in itself preclude the use of organic or monomer solublecatalysts as demonstrated by the effectiveness of such initiators insuspension and emulsion polymerization processes. Nevertheless, monomersoluble catalysts such as benzoyl peroxide, tertiary butylperoxypivalate and azobisisobutyronitrile are ineffective in the processof the present invention in that they yield random copolymers incontrast to the equimolar, alternating copolymers produced in thepresence of a water-soluble catalyst.

The water-soluble free radical initiators which are effective in theprocess of the present invention include water-soluble peroxygencompounds such as perborates, percarbonates, persulfates, perchlorates,peracids, peroxides, and the like. Such initiators include ammonium andpotassium persulfate, peracetic acid and hydrogen peroxide.

The water-soluble free radical initiators are generally effective in thepresent invention at temperatures below those at which they areeffective in emulsion or aqueous solution polymerization. Thus, whereasammonium persulfate is generally used in emulsion polymerization attemperatures of 50C. and above, it is effective at 30C. in the processof the present invention. The concentration of free radical initiatorsgenerally ranges 0.00l to ID weight percent based on monomerconcentrations.

The use of redox systems permits the reaction to be carried outeffectively either at lower temperatures or with lower initiatorconcentrations. Such redox systems include potassium persulfate-sodiumbisulfite, ammonium persulfatesodium thiosulfate, ammoniumpersulfate-ferrous ammonium sulfate and potassium permanganate-oxalicacid. Other redox systems such as are conventionally used in emulsionand aqueous solution polymerization are generally effective in thepresent invention.

The temperature of polymerization may be as low as C. or as high asl()0C. However, the preferred temperature range is from to 70C. Thelower the ratio of electron acceptor monomer to Friedel-Crafts catalystthe lower the preferred temperature. The temperature of polymerizationis selected as a result of consideration of the temperature at which thefree radical precursor generates free radicals at a sufficient rate topromote rapid polymerization. A further consideration is the temperatureat which the Friedel-Crafts catalyst undergoes hydrolysis in the aqueousmedium and is converted to an ineffective complexing agent.

The process of the instant invention may be carried out on a continuousbasis or as a batch process by the usual techniques known to one skilledin the art. In one embodiment of the process, the Friedel-Craftscatalyst and water are charged to the reactor, followed by thecomonomers and the water-soluble free radical percursor or thecomponents of the redox catalyst system. The reaction is then carriedout for the desired period of time at the preferred temperature. Thereaction is then terminated by the addition of methanol whichdeactivates the Fried'el-Crafts catalyst. Where the reaction isconducted with an excess of one of the monomers which acts as a solventfor the alternating copolymer, the methanol also precipitates thecopolymer from the reaction mixture. Treatment of the precipitatedcopolymer with ammoniacal methanol results in the removal of theinorganic residues from the Friedel- Crafts catalyst, and yields acopolymer with little or no ash content. The copolymer may be furtherpurified by solution in a suitable solvent such as acetone andreprecipitation with methanol.

in another embodiment of the process, the Friedel- Crafts catalyst isadded in several portions throughout the reaction period. This isparticularly useful where high conversions are desired in a batchprocess since the insolubility of the copolymer in the aqueous mediumresults in entrappment of the Friedel-Crafts catalyst in theprecipitated copolymer mass and reduces its availability to theunreacted comonomers.

In a further embodiment of the process, the watersoluble free radicalprecursor or the redox catalyst is added in several portions throughoutthe reaction period. This permits better control of the temperature inthe exothermic reaction.

By the use of one of these embodiments of the instant process and byother variations which are obvious to one skilled in the art, it ispossible to obtain equimolar, alternating copolymers in essentiallyquantitative yield based upon in equimolar comonomer charge. When one ofthe comonomers is charged in excess of an equi molar amount, the excessdoes not participate in the formation of the equimolar, alternatingcopolymer which may be obtained in essentially quantitative yield basedon equimolar amounts of the comonomers.

The equimolar composition and alternating structure of the copolymersproduced by the process of the instant invention may be confirmed byelemental analyses and/or nuclear magnetic resonance (NMR) spectroscopy.

The acrylonitrile and other nitrogen-containing monomer content of thecopolymers may be determined from the nitrogen analysis. Since elementalanalyses are considered acceptable when the observed analysis is within0.5 percent absolute of the theoretical analysis, conversion of thenitrogen analysis to monomer content results in the latter rangingwithin :3 percent of the true value. Thus, an acrylonitrile content of47-53 percent is considered indicative of an equimolar copolymer. Sincethe random copolymer prepared from an equimolar mixture of styrene andacrylonitrile in the presence of a free radical catalyst contains 40percent acrylonitrile, there is no difficulty in distinguishing theequimolar, alternating copolymer of the instant process from the randomcopolymer.

The unequivocal determination of polymer structure is based on the NMRanalysis. The absence of donor monomer-doner monomer and acceptormonomeracceptor monomer diads in the NMR spectrum confirms thealternating structure and hence the equimolar composition of thecopolymers of the instant process. The absence of styrene-styrene andacrylonitrileacrylonitrile diads in the NMR spectra of thestyreneacrylonitrile copolymers prepared by the process of the instantinvention confirms the assignment of alternating structure and equimolarcomposition to the copolymers whose nitrogen analyses indicate thepresence of 47-53 percent acrylonitrile.

The content of oxygen-containing monomer such as acrylic or methacrylicacid or ester in the copolymers may be determined from the carbon,hydrogen and/or oxygen analysis. However, in the case of styrenemethylmethacrylate copolymers prepared with an equimolar comonomer charge,elemental analyses serve to indicate the equimolar composition but areinsufficient to confirm the alternating structure since an equimolar,random copolymer would be formed from a radical polymerization in theabsence of the Friedel- Crafts catalyst. in this case, the absence ofstyrenestyrene and methyl methacrylate-methyl methacrylate diads in theNMR spectrum confirms the alternating structure,

The following examples are representative of the methods which areuseful in the practice of this invention and should not be considered inany matter as limiting the scope thereof.

POLY( STYRENE-ALT-ACRYLON lTRlLE) EXAMPLE 1 A 3-necked, 500 ml. flaskequipped with stirrer, thermometer and nitrogen inlet and outlet wascharged with 29.6 ml. of water and 12.8 g. of zinc chloride. A mixtureof 19.6 g. of styrene and 10.0 g. of acrylonitrile was then added,followed by 2.7 g. of potassium persulfate. The styrene/acrylonitrilemolar ratio was 1/1 and the acrylonitrile/zinc chloride molar ratio was2/1. The temperature was elevated to 40C. and maintained at 40C. forhours. The reaction was terminated by pouring the reaction mixture intomethanol. The precipitated copolymer was filtered and stirred withammoniacal methanol. This process was repeated three times withconcentrated aqueous ammonia and the precipitate was finally filteredand washed with methanol. The product was dissolved in acetone andreprecipitated with methanol. The recovered copolymer was dried at 40C.in vacuo. The yield of copolymer was 3.62 g., representing a monomerconversion of 12.2 percent. Elemental analysis indicated a nitrogencontent of 9.05 percent corresponding to 50.8 molepercent acrylonitrile.The product was therefore an equimolar styrene-acrylonitrile copolymer.A conventional free radical copolymerization would be expected to yielda 60/40 styrene-acrylonitrile copolymer from an equimolar charge. TheNMR spectrum recorded in CDCI at 70C. indicated the absence ofstyrenestyrene and acrylonitrile-acrylonitrile diads, confirming thealternating structure of the equimolar copolymer. The intrinsicviscosity of the copolymer was 1.65 dl./g. in dimethylformamide at 30C.

EXAMPLE 2 When a similar reaction as described in Example 1 was carriedout at 50C. for 1 hour the yield of copolymer was 1.2 g., representing amonomer conversion of 4.1 percent. The product contained 48.6mole-percent acrylonitrile and its alternating structure was confirmedby NMR analysis. The equimolar copolymer had an intrinsic viscosity of1.085 dl./g. in DMF at 30C.

EXAMPLE 3 When a similar reaction as described in Example 1 was carriedout at 30C. for 30 minutes using 0.55 g. of potassium persulfate and 0.1l g. of sodium meta bisulfite as initiating system, the equimolaralternating copolymer (nitrogen and NMR analyses) was obtained in ayield of l 1.9 g., representing a monomer conversion of 40.0 percent.The intrinsic viscosity in DMF at 30C. was 2.27 dl./g.

EXAMPLE 4 A 500 ml. flask was charged with 28.3 g. of water and 12.24 g.of zinc chloride. The mixture was stirred until the zinc chloridedissolved and then 9.54 g. of acrylonitrile and 43.7 g. of styrene wereintroduced. The styrene/acrylonitrile molar ratio was 7/3 and theacrylonitrile/zinc chloride molar ratio was 2/1. A mixture of 0.81 g. ofpotassium persulfate and 0.18 g. of sodium bisulfite was introduced andthe reaction was carried out at 30C. for 20 hours. The reaction wasterminated by the addition of methanol containing hydroquinone. Theproduct was filtered, stirred with ammoniacal methanol and againfiltered. After solution in acetone and precipitation into a largeexcess of methanol. the recovered copolymer was dried in vacuo at 40C.for 16 hours. The yield of copolymer was 23.35 g., representing amonomer conversion of 82.6 percent when calculated on the basis of anequimolar styrene/acrylonitrile composition. Elemental analysesindicated the product contained 83.64 percent carbon, 7.07 percenthydrogen and 9.24 percent nitrogen which corresponds to a 48.5/51.5styrene/acrylonitrile composition. A free radical copolymer obtainedfrom the same comonomer charge would have had a 65.5/34.5styrene/acrylonitrile composition. The equimolar composition andalternating structure of the copolymer was confirmed by NMR analysis.

When a similar reaction was carried out at 30C. for 30 hours, the yieldof equimolar, alternating copolymer was quantitative, based upon anequimolar styrene/acrylonitrile composition.

EXAMPLE 5 A 3-necked 300 ml. flask was charged with 15.7 ml. of waterand 2.3 g. zinc chloride. A mixture of 5.3 g. of acrylonitrile and 10.4g. of styrene was added. followed by 0.27 g. of potassium persulfate and0.05 g. of sodium bisulfite. The styrene/acrylonitrile mole ratio was1/1. The reaction mixture was stirred under nitrogen at 25C. for 4hours. After the addition of 2.3 g. of zinc chloride stirring wascontinued at 25C. for another 4 hours. An additional 2.2 g. of zincchloride was then added and stirring continued at 25C. for 16 hoursmaking a total reaction time of 24 hours. The acrylonitrile/zincchloride mole ratio was 2/1. The reaction product was isolated byprecipitation with methanol. After solution in acetone and precipitationwith methanol, the product was dried in vacuo. The yield of copolymerwas 12.9 g. representing a monomer conversion of 82.1 percent. Carbon,hydrogen and nitrogen analyses indicated that the copolymer had a 50/50styrene/acrylonitrile composition. NMR analysis confirmed thealternating structure of the copolymer.

EXAMPLE 6 A mixture of 25.0 g. of styrene and 8.5 g. of acrylonitrilewas added to a solution of 10.9 g. of zinc chloride in 25.1 ml. ofwater. The styrene/acrylonitrile mole ratio was 6/4 and theacrylonitrile/zinc chloride mole ratio was 2/1. After the addition of0.55 g. of potassium persulfate and 0.11 g. of sodium metabisulfite, thereaction mixture was stirred under nitrogen at 30C. for 2 hours. Thereaction was terminated by the addition of methanol. The precipitatedcopolymer was filtered, dissolved in acetone and reprecipitated withmethanol. The dried copolymer weighed 14.0 g., representing a monomerconversion of 56.0 percent. Elemental analyses indicated that thecopolymer had a 51/49 styrene/acrylonitrile composition while theabsence of styrene/styrene and acrylonitrile-acrylonitrile diads in theNMR spectrum confirmed the alternating structure of the equimolarcopolymer.

EXAMPLE 7 A S-necked 300 ml. flask was charged with 31.4 ml. of waterand 20.3 g. of magnesium chloride hexahydrate. A mixture of 20.8 g. ofstyrene and 10.6 g. of acrylonitrile was added, followed by 2.28 g. ofammonium persulfate. The styrene/acrylonitrile mole ratio was Ill andthe acrylonitrile/magnesium chloride mole ratio was 2/1. The reactionmixture was stirred under nitrogen at 40C. for 3 hours. The reactionproduct was isolated by precipitation with methanol. washed with ammoniaseveral times, and, after a final wash with methanol. dried in vacuo.The yield of copolymer was 1.32 g. representing a monomer conversion of4.2 percent. The nitrogen content was 9.10 percent indicating anacrylonitrile content of 51.1 percent. The alternating structure of theequimolar copolymer was confirmed by NMR analyses.

EXAMPLE 8 The reaction described in Example 7 was carried out in thepresence of 23.7 g. of nickel chloride hexahydrate. The yield ofcopolymer was 1.10 g. The nitrogen content of 8.64 percent indicated astyrene/acrylonitrile mole ratio of 51.4/48.6 and NMR analysis confirmedthe formation of an equimolar, alternating copolymer.

POLY(STYREN E-ALT-METHYL METHACRYLATE) EXAMPLE 9 An aqueous Zincchloride solution was prepared by dissolving 13.6 g. of zinc chloride in41.0 ml. of water. A mixture of 20.0 g. of methyl methacrylate and 20.8g. of styrene was added, followed by 0.55 g. of potassium persulfate and0.11 g. of sodium metabisulfite. The styrene/methyl methacrylate moleratio was l/l and the methyl methacrylate/zinc chloride mole ratio was2/1. The reaction was carried out under nitrogen with stirring for 4hours at 30C. The product was precipitated with methanol, filtered,dissolved in benzene and reprecipitated with methanol. The yield ofcopolymer was 3.8 g. representing a monomer conversion of 9.3 percent.Elemental analyses indicated that the product was an equimolar copolymerwhile the absence of styrene-styrene and methyl methacrylate-methylmethacrylate diads in the NMR spectrum confirmed the alternatingstructure of the copolymer.

EXAMPLE 10 The copolymerization of 10.4 g. of styrene and 10.0 g. ofmethyl methacrylate (styrene/methyl methacrylate mole ratio l/l in thepresence of 20.4 ml. of water and 13.6 g. of zinc chloride (methylmethacrylate/zinc chloride mole ratio 1/1) was carried out at 25C. using0.27 g. of potassium persulfate and 0.05 g. of sodium bisulfite as redoxcatalyst. After 23 hours. the reaction was terminated by precipitationwith methanol. The yield of copolymer was 4.2 g. representing a monomerconversion of 20.6 percent. Oxygen analysis and the NMR spectrumconfirmed the equimolar composition and the alternating structure of thecopolymer, respectively.

POLY(STYRENE-ALT-BUTYL ACRYLATE) EXAMPLE l 1 A mixture of 12.8 g. ofbutyl acrylate and 10.4 g. of styrene was added to a flask which hadpreviously been charged with 23.2 g. of water and 13.6 g. of zincchloride. The styrene/butyl acrylate mole ratio was l/l and the butylacrylate/zinc chloride mole ratio was l/l. The redox catalyst consistingof 0.27 g. of potassium persulfate and 0.05 g. of sodium bisulfite wasadded and the reaction mixture was stirred at 25C. for 3 hours. Theyield of copolymer. obtained by precipitation with methanol, solution inbenzene and reprecipitation in methanol, was 1.13 g. representing aconversion of 4.9 percent. Elemental analyses of the copolymer gavevalues of 78.34 percent carbon, 8.31 percent hydrogen and 13.29 percentoxygen which corresponds to a 48/52 styrene/butyl acrylate composition.

When the reaction was carried out at 25C. for 20 hours the yield ofcopolymer was increased to 1.82 g. representing a conversion of 7.9percent. The elemental analyses of 77.64 percent carbon, 8.24 percenthydrogen and 14.21 oxygen indicated a 49/51 styrene/butyl acrylatecomposition.

NMR analyses of the copolymers obtained after 3 hours and after 20 hoursconfirmed the alternating structure of both copolymers.

POLY lSOPRENE-ALT-ACRYLONlTRlLE) EXAMPLE 12 A 250 ml. flask was chargedwith 26 ml. of water and 60 g. of zinc chloride. After the aqueoussolution was heated to 40C., a mixture of 30 g. of isoprene and 10 g. ofacrylonitrile was added, followed by 0.15 g. of potassium persulfate.The isoprene/acrylonitrile mole ratio was /30 and the acrylonitrile/zincchloride mole ratio was 0.43. The reaction mixture was maintained at40C. for 1 hour. The copolymer was isolated by precipitation withmethanol and after washing with ammonia and methanol was obtained in ayield of 2.0 g. This represented a yield of l 1.0 percent whencalculated on the basis of a 1:1 isoprene/acrylonitrile composition.Nitrogen analysis indicated an acrylonitrile content of 5 l .3mole-percent, confirming the equimolar composition of the copolymer. Thealternating structure was confirmed by NMR analysis.

EXAMPLE 13 When a similar reaction as described in Example 12 wascarried out at 40C. for 3 hours the yield of copolymer was 2.8 g.representing a 12.2 percent yield on the basis of a 1:1isoprene/acrylonitrile composition. The nitrogen analysis indicated a47.8/52.2 isoprene/acrylonitrile molar composition. NMR analysisdemonstrated the alternating structure of the equimolar composition bythe absence of isoprene-isoprene and acrylonitrile-acrylonitrile diads.

EXAMPLE 14 A mixture of 4.6 g. of isoprene and 31.8 g. of acrylonitrilewas added to a solution of 60 g. of zinc chloride in 26 ml. of water at50C. The isoprene/acrylonitrile mole ratio was 10/90 and theacrylonitrile/zinc chloride mole ratio was 1.35. After the addition of0. 1 5 g. of potassium persulfate the reaction mixture was maintained at50C. for 2 hours. The copolymer yield of 1.2 g. represented a 16.8percent yield on the basis of an equimolar composition. The alternatingstructure and equimolar composition were confirmed by elemental and NMRanalyses.

POLY( BUTADlENE-A LT-ACRYLONlTRlLE) EXAMPLE 15 The reaction of 5.4 g. ofbutadiene and 26.5 g. of acrylonitrile in the presence of 6.8 g. of zincchloride in 10.7 g. of water. using 0.27 g. of potassium persulfate and0.05 g. of sodium bisulfite as redox catalyst system. was carried out ina bottle at 25C. for 20 hours. The butadiene/acrylonitrile mole ratiowas 1/5 and the acrylonitrile/zinc chloride mole ratio was 10/1. Therubbery precipitate obtained on the addition of methanol weighed 3.48 g.after drying, representing a monomer conversion of 32.5 percent based onan equimolar composition. The latter was confirmed by the 13.0 percentnitrogen content of the copolymer which indicated a 51/49butadiene/acrylonitrile composition. The absence of butadiene-butadieneand acrylonitrileacrylonitrile diads in the NMR spectrum also confirmedthe equimolar, alternating nature of the copolymer.

POLY(BUTADlENE-ALT-BUTYL ACRYLATE) EXAMPLE 16 A bottle was charged with18.2 g. of water, 13.6 g. of zinc chloride, 64.0 g. of butyl acrylateand 5.4 g. of butadiene. The butadiene/butyl acrylate mole ratio was l/5and the butyl acrylate/zinc chloride mole ratio was 5/1. After theaddition of 0.27 g. of potassium persulfate and 0.05 g. of sodiumbisulfite. the bottle was shaken at 25C. for 20 hours. The productisolated by precipitation with methanol, after drying. weighed 2.2 g.representing a 12.1 percent conversion basedon an equimolar composition.The elemental analyses of the copolymer indicated 72.33 percent carbon,10.01 percent hydrogen and 17.81 percent oxygen which corresponds to a49/51 butandiene/butyl acrylate composition. The equimolar, alternatingstructure of the copolymer was confirmed by NMR analyses.

POLY(lSOBUTYLENE-ALT-BUTYL ACRYLATE) EXAMPLE 17 A bottle was chargedwith 18.4 g. of water and 13.6 g. of zinc chloride. Following theaddition of 12.8 g. of butyl acrylate, the bottle was purged withnitrogen and cooled to C. After the addition of 0.54 g. of potassiumpersulfate and 0.10 g. of sodium bisulfite, 28.0 g. of isobutylene wascondensed in the bottle which was then sealed. The isobutylene/butylacrylate mole ratio was /1 and the butyl acrylate/zinc chloride moleratio was l/l The bottle was shaken at 0C. for 20 hours and the contentswere then precipitated with methanol. The dried copolymer weighed 3.3 g.representing a 17.9 percent conversion based on an equimolarcomposition. Based on carbon, hydrogen and oxygen analyses the copolymerwas demonstrated to have an equimolar isobutylene/butyl acrylatecomposition. The alternating structure of the copolymer was confirmed byNMR analyses.

The above examples demonstrate that the process of the instant inventioncan readily be employed to produce equimolar, alternating copolymers.

Numerous advantages result from the use of an aqueous medium forcarrying out the copolymerization reaction. The most obvious advantageis the use of a reaction medium which is readily obtained free ofinhibiting impurities and does not require the extensive purificationand recovery required when an organic solvent is used. The preferredwater-soluble initiators, including redox systems, can be readily storedand handled at ordinary temperatures and yet can be used at lowtemperatures. In contrast, the solvent or monomer-soluble initiatorswhich can be used at low temperatures require special storage andhandling. Further, since the copolymers produced by the instant processare substantially insoluble in water, product isolation is simplified bythe elimination of the organic diluents employed in the prior artprocesses.

While particular embodiments of this invention are shown above, it willbe understood that the invention is obviously subject to variations andmodifications without departing from its broader aspects.

What is claimed is:

1. In a process for preparing equimolar alternating copolymers bycopolymerization of a hydrocarbon electrondonating monomer consisting ofconjugated dienes with an electron accepting monomer selected from thegroup consisting of alkyl and aryl acrylates and methacrylates,acrylonitrile and methacrylonitrile, the improvement which comprisescarrying out said copolymerization at a temperature within the range ofabout 0 to C., in an aqueous medium containing 0.01 to 5 moles per moleof electron accepting monomer of a Friedel-Crafts halide which is atleast divalent and stable to hydrolysis at the reaction temperature and0.001 to 10 percent by weight based on the weight of the monomers of awater-soluble peroxygen compound free radical initiator.

2. 1n the process of claim 1 wherein said conjugated diene is selectedfrom the group consisting of butadiene and isoprene.

3. 1n the process of claim 1 wherein said acrylic nitrile isacrylonitrile.

4. 1n the process of claim 1 wherein said methacrylic ester is methylmethacrylate.

5. In the process of claim 1 wherein said electron accepting monomer isbutyl acrylate.

6. ln the process of claim 1 wherein said Friedel- Crafts halide isselected from the group consisting of zinc chloride, magnesium chlorideand nickel chloride.

7. In the process of claim 1 wherein said peroxygen compound ispersulfate.

8. 1n the process of claim 1 wherein said free radical initiator is aredox system.

9. In the process of claim 8 wherein said redox system consists of apersulfate and a bisulfite.

1. IN A PROCESS FOR PREPARING EQUIMOLAR ALTERNATING COPOLYMERS BYCOPOLYMERIZATIN OF A HYDROCARBON ELECTRON DONATING MONOMER CONSISTING OFCONJUGATED DIENES WITH AN ELECTRON ACCEPTING MONOMER SELECTED FROM THEGROUP CONSISTING OF ALKYL AND ARYL ACRYLATES AND METHACRYLATES,ACRYLONITRILE AND METHACRYLONITRILE, THE IMPROVEMENT WHICH COMPRISESCARRYING OUT SAID COPOLYMERIZATION AT A TEMPERATURE WITHIN THE RANGE OFABOUT 0* TO 100*C., IN AN AQUEOUS MEDIUM CONTAINING 0.01 TO 5 MOLES PERMOLE OF ELECTRON ACCEPTING MONOMER OF A FRIEDEL-CRAFTS HALIDE WHICH ISAT LEAST DIVALENT AND STABLE TO HYDROLYSIS AT THE REACTION TEMPERATUREAND 0.001 TO 10 PERCENT BY WEIGHT BASED ON THE WEIGHT OF THE MONOMERS OFA WATER-SOLUBLE PEROXYGEN COMPOUND FREE RADICAL INITIATOR.
 2. In theprocess of claim 1 wherein said conjugated diene is selected from thegroup consisting of butadiene and isoprene.
 3. In the process of claim 1wherein said acrylic nitrile is acrylonitrile.
 4. In the process ofclaim 1 wherein said methacrylic ester is methyl methacrylate.
 5. In theprocess of claim 1 wherein said electron accepting monomer is butylacrylate.
 6. In the process of claim 1 wherein said Friedel-Craftshalide is selected from the group consisting of zinc chloride, magnesiumchloride and nickel chloride.
 7. In the process of claim 1 wherein saidperoxygen compound is persulfate.
 8. In the process of claim 1 whereinsaid free radical initiator is a redox system.
 9. In the process ofclaim 8 wherein said redox system consists of a persulfate and abisulfite.